Page 981 - Veterinary Immunology, 10th Edition

Eosinophils have many PRRs that recognize PAMPs and DAMPs.
VetBooks.ir When triggered, eosinophils release multiple cytokines,

chemokines, and their granule contents. Although eosinophils can
phagocytose small particles, they are much more suited to

extracellular destruction of large parasites since they can
degranulate into the surrounding fluid. Eosinophils may release
intact granules by exocytosis, or, more commonly, undergo
piecemeal degranulation. In this process, small vesicles bud off the

secondary granules and are released into the extracellular tissues.
This occurs in response to IgE-coated parasites, many chemokines,
PAF, and C5a. Once free in extracellular fluid, eosinophil granules
can function as independent structures capable of secreting granule

proteins in response to IFN-γ or CCL11. Activated eosinophils can
also eject extracellular traps containing mitochondrial DNA and
granule cationic proteins. They do this in response to bacterial
products such as endotoxins. The release of these nets is not

accompanied by cell death.
Eosinophils contain two types of granules (see Figs. 29.15 and
29.16). Their small, primary granules contain arylsulfatase,
peroxidase, and acid phosphatase. Their large crystalloid granules

have a core of major basic protein (MBP) surrounded by a matrix
containing eosinophil cationic protein (ECP), eosinophil peroxidase
(EPO), and eosinophil-derived neurotoxin (EDN) (Fig. 29.18).
Eosinophils also produce lipid mediators such as leukotrienes and

PAF. Particles bound to eosinophil receptors trigger a powerful
respiratory burst. The EPO uses bromide in preference to chloride,
thus producing OBr-. It also generates nitric oxide and
nitrotyrosine, both potent oxidizing agents. Eosinophil granule

proteins can kill helminths and bacteria and are important
mediators of tissue pathology. They all, for example, damage
respiratory epithelium. The production by eosinophils of multiple
Th2 cytokines (Table 29.3) as well as indoleamine dioxygenase

inhibits local Th1 responses and ensures that a “Th2 environment”
is maintained where eosinophils accumulate.

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